Apparatus for producing alternating current from brushless dc motor



jan- 13, L. KATZ APPARATUS FOR PRODUCING ALTERNATING CURRENT FROMBRUSHLESS DC MOTOR Filed Jan. 11, 1966 ALTfiNATE PHA SE INVENTORLEONHARD KATZ ATTORNEYS United StatesPatent O US. Cl. 318-138 ClaimsABSTRACT OF THE DISCLOSURE Multi-phase generator of DC utilizingbrushless DC motor, the DC being derived, for example, directly from theprimary winding of a push-pull drive circuit or from the starter windingafter starting of the motor.

The present invention relates to the production of alternating currentfrom direct-current motors and the like; and, more particularly, frombrushless motors of the solid-state switching (inverter) type describedin my prior U.S. Letters Patent No. 3,098,958, issued July 23, 1963.

The production of alternating-current voltage from direct-current motorapparatus and the like, and, more specifically, mutli-phasealternating-current voltage, has long been considered a most desirable,but economically and otherwise impractical, solution of certain powersup ply problems, as, for example, in aircraft and other vehicles andthe like. It is to a most satisfactory and unexpectedly eificient andfacile solution of such problems that the present invention isaccordingly directed; it having been discovered that brushlessdirect-current motors of the above-described type may be simply modifiedto operate simultaneously also for the production of multiphasealternating-current voltage.

An object of the invention, accordingly, is to provide a new andimproved apparatus for producing single and multi-phasealternating-current voltage with the aid of direct-current motorapparatus and the like (the term motor being generically employed hereinto connote not only such apparatus in which a rotor is rotated, but inwhich other loads are controlled by the system); preferably, though notexclusively, motors of the brushle'ss solid-state switching (inverter)type above mentioned.

A further object is to provide a new and improved apparatus forproducing alternating-current power of more general application and use,as well.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in connection with the appended claims.

The invention will now be described with reference to the accompanyingdrawings, FIG. 1 of which is a schematic circiut diagram of a preferredembodiment;

FIG. 2 is a partial circuit diagram of a modification;

FIG. 3 is still a further partial circuit of a further modification; and

FIG. 4 is a diagrammatic drawing of an additional modified structure.

Referring to FIG. 1, the invention is described for illustrativepurposes in connection with the preferred solid-state switching relaybrushless motor circut of the type disclosed in said Letters Patent,though clearly other types of such circuits can, if desired, beemployed. The inverter circuits of two such motors are those illustratedat I and I embodying respective similar stator windings S and S orientedin proximity to one another and at a geometrical angle of ninetydegrees. The rotor coupled to the stator windings is not illustrated inorder to avoid confusing the diagram. The motor circuit I employs a pairof push-pull connected switching relays Q and Q such as solid-statetransistor devices, con

trolled rectifiers, or the like, each shown having respective baseelectrodes .1, 3, collectors 5, 7, and emitters 9, 11. A capacitor Cshunts the terminals of the stator winding S between the collectors 5and 7, with the emitters 9 and 11 connected together to the negativeterminal of a direct-current source the positive terminal of which isconnected to an intermediate tap of the stator winding S. Steeringdiodes D and D are respectively connected between the collector andemitter electrodes of each relay device. Switchingoscillation-sustaining feedback winding F, coupled to the stator S, isconnected at its terminals to the bases 3 and 1 of switching relays Qand Q, with an intermediate tap connected through resistance R to thenegative terminal all as described in the said Letters Patent. Thesimilar components of motor circuit I are designated by the samereference numerals, but with a prime notation.

Such coupled motor circuits I and I have been found to operateefficiently and in locked relationship, with speed control available by,for example, application of a control signal variation at terminal T ofthe feedback winding F. A timing circuit for controlling starting may beconnected at terminals T and T to respective siliconcontrolledrectifiers SCR and SCR or similar gating devices, connected to oppositeterminals of stator winding S and to starting winding W and capacitor CIt has been discovered that by coupling a substantially resistive load Land/ or L) to the stator winding S (and/ or S), as by direct electricalconnections 24 (and/or 24) to the opposite terminals thereof, effectivealternating-current energization of the load L (and/or L) is effected.The alternating-current voltage in the load circuit 2-L-4, moreover, hasbeen found to be in the same phase angle relationship to that in theload circuit 2-L 4 as the geometrical angle between stator windings Sand S; in this case, ninety degrees.

Thus, multi-phase alternatingcurrent voltage may be produced in thismanner, with the direct-current motors still simultaneously useful fortheir motor-driving functions, if desired. If sixty-degreemultiple-phase alternating current is desired, three such motor circuitsI, I and I may be similarly employed, oriented in sixty degreegeometrical relationship, as shown by their respective stator windingsS, S and S in FIG. 2.

In actual practice, a standard 118 LEM motor of the type shown in FIG.1, marketed by Astro Dynamics, Inc. of Burlington, Mass., has been usedto operate resistances and light bulbs connected at L and L' (of 40 ohmscold resistance) with a total power of 40 watts, and with a motor inputof 2 amps and 28 volts at no load. It has further been found that,fortuitously, none of (a) the ninety-degree phase relationship betweenthe alternatingcurrent voltages applied to the load circuits 2L-4 and2L-4, (b) the amplitude or frequency of the substan tially squarewave-shape voltage, or (c) the speed of the motor, changed significantlywith variation between no load and full load conditions, thus providinga most stable and useful alternating-current source.

It has further been found that, after starting, once the motor is up tospeed, ganged switches 8 -8 (FIG. 3) may be activated to disconnect thestarting winding W from the circuit and to connect it with loadresistance, including a lamp, to supply the same withalternating-current power, also. Thus, though there is no directelectrical connection to the power stator winding, the magnetic couplingenables alternating-current power to be supplied. Secondary windingsmagnetically coupled to the stator windings may thus also be used foralternating-current power production, with such windings geometricallyoriented to provide the desired multiphases.

It has been noted that in single-phase motors, the start phase has asinusoidal wave shape, even when the main phase has a square wave shape.This may be used to advantage in the arrangement of FIG. 4 wheremulti-phase windings 10, etc. (coupled to the same rotor bars R as themain and alternate-phase windings, so-labelled) may be spaced evenly orotherwise around the periphery of the common rotor R.

Further modifications will also occur to those skilled in the art andall such are considered to fall within the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

1. Apparatus for producing alternating-current from direct-current andcomprising, in combination, a rotor, at least a pair of stator windingsdisposed at a predetermined angle from one another and coupled to saidrotor, each of said stator windings having a pair of switching relaysconnected in push-pull with the associated winding to comprise anoscillator circuit for sustaining switching oscillations in the statorwinding, alternating-current load means, and means for coupling to saidload means oscillations from said stator windings, respectively, havingelectrical phase the same as the space phase of said windings relativeto each other, said apparatus being ,devoid of a phase control circuitinterconnecting said windings and said oscillations being produced inthe absence of the application of alternating-current to said apparatusfrom an external source.

2. Apparatus as claimed in claim 1, and in which the coupling meanscomprises electrical connections to terminals of the stator windings.

3. Apparatus as claimed in claim 1 in which the coupling means comprisesfurther windings magnetically cou- .4 pled to the stator windings andconnected with the load means.

4. Apparatus as claimed in claim 3, and in which the further windingscomprise a plurality of secondary windings and the load means comprisesa corresponding plurality of load circuits connected thereto.

5. Apparatus as claimed in claim 1, and in which the said angle is oneof substantially 90 degrees and degrees.

References Cited UNITED STATES PATENTS 2,097,577 11/1937 Seitner 307-4563,090,897 5/1963 Hammann 318138 3,146,388 8/1964 Rasor 318138 3,341,7239/1967 Tourtellot 31068 3,044,023 7/1962 Floyd 331113.1 XR 3,141,1107/1964 Corry 3212 XR 3,175,167 3/1965 Lloyd 318138 XR 3,235,818 2/1966Meszaros et a1. 3212 XR 3,319,104 5/1967 Yasuoka et al 318--1383,321,687 5/1967 Toth 331-1131 XR 3,321,688 5/1967 Vondelden 318138OTHER REFERENCES Soviet Inventions Illustrated, March 1963, p. 10.

ORIS L. RADER, Primary Examiner G. R. SIMMONS, Assistant Examiner US.Cl. X.R.

